Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | The Cryosphere Discuss., 7, 4937–4976, 2013 Open Access www.the-cryosphere-discuss.net/7/4937/2013/ The Cryosphere TCD doi:10.5194/tcd-7-4937-2013 Discussions © Author(s) 2013. CC Attribution 3.0 License. 7, 4937–4976, 2013 This discussion paper is/has been under review for the journal The Cryosphere (TC). Surge dynamics in Please refer to the corresponding final paper in TC if available. the Nathorstbreen glacier system Surge dynamics in the Nathorstbreen M. Sund et al. glacier system, Svalbard Title Page M. Sund1,2, T. R. Lauknes3, and T. Eiken4 Abstract Introduction 1Norwegian Water Resources and Energy Directorate, P.O. Box 5091 Majorstuen, 0301 Oslo, Norway Conclusions References 2University Centre in Svalbard, P.O. Box 156, 9171 Longyearbyen, Norway 3Norut P.O. Box 6434 Forskningsparken, 9294 Tromsø, Norway Tables Figures 4University of Oslo, P.O. Box 1047 Blindern, 0316 Oslo, Norway J I Received: 5 September 2013 – Accepted: 21 September 2013 – Published: 8 October 2013 Correspondence to: M. Sund ([email protected]) J I Published by Copernicus Publications on behalf of the European Geosciences Union. Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion 4937 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Abstract TCD Nathorstbreen glacier system (NGS) recently experienced the largest surge in Svalbard since 1936, and is examined using spatial and temporal observations from DEM differ- 7, 4937–4976, 2013 encing, time-series of surface velocities from satellite synthetic aperture radar (SAR) 5 and other sources. The upper basins with maximum accumulation during quiescence Surge dynamics in correspond to regions of initial lowering. Initial speed-up exceeds quiescent velocities the Nathorstbreen by a factor of several tens of times. This suggests that polythermal glaciers surges glacier system are initiated in the temperate area before mass is displaced downglacier. Subsequent downglacier mass displacement coincides with areas of 100–200 times increased ve- M. Sund et al. 10 locities (stage 2). After > 5 yr the joint NGS terminus advanced abruptly into tidewater during winter. The advance was followed by upglacier propagation of crevasses, indi- cating a re-action following from the already displaced mass and extending flow. NGS Title Page advanced ca. 15 km, while another ca. 3 km length was lost due to calving. Surface Abstract Introduction lowering of ca. 50 m was observed in some upglacier areas and during 5 yr the to- −1 15 tal area increased by 20 %. Maximum measured flow rates were at least 25 m d , Conclusions References 2500 times quiescence, while average velocities were about 10 m d−1. The surges of Tables Figures Zawadzkibreen cycle with ca. 70 yr periods. J I 1 Introduction J I Svalbard is one of the areas with the densest population of surge-type glaciers. Still Back Close 20 relatively few glacier surges here have been studied in detail, especially covering both the entire quiescent and surge phase (Murray et al., 2012; Sund and Eiken, 2004). The Full Screen / Esc mechanism behind glacier surging has been studied for several decades, but still the exact cause of glacier surging remains an unsolved question. Remote sensing tech- Printer-friendly Version niques however, have improved the temporal and spatial data resolution and enables Interactive Discussion 25 new perceptions on glacier dynamics. In this paper we mainly use satellite remote sensing data acquired between 1992 and 2012 to investigate the surge dynamic of the 4938 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | different glaciers in the Nathorstbreen glacier system (NGS), during the largest surge in Svalbard since 1936. TCD Glacier surges occur as quasi-cyclic rapid velocity accelerations of 10–1000 times 7, 4937–4976, 2013 the glacier velocity during the longer quiescent phases. Fast flow is associated with a 5 large basal motion component (e.g. Clarke, 1987). The events are triggered by internal rather than external dynamic processes. In the course of the surges large masses of Surge dynamics in ice are transferred from higher to lower parts of the glacier. During build-up the glacier the Nathorstbreen surface gradient increases. Surges are found both in land- and tidewater terminating glacier system glaciers as well as temperate and polythermal ones (Meier and Post, 1969; Dolgo- M. Sund et al. 10 ushin and Osipova, 1975; Clarke et al., 1987; Cuffey and Patterson, 2010). Based on studies from the temperate Variegated Glacier, Alaska a hydraulic mechanism, where surges were explained by switches between fast tunnel based basal drainage and slow Title Page linked-cavity system, was proposed (Kamb et al., 1985; Kamb, 1987). Some glaciers displaying abrupt speed-up and slow down, while other glaciers go through slower Abstract Introduction 15 accelerations and decelerations. Differences in observed surge characteristics and dy- namics have also lead to a suggestion of at least two separate surge mechanisms Conclusions References between polythermal and temperate glaciers (Murray et al., 2003a). Surges in polyther- Tables Figures mal glaciers were explained by changes in basal thermal regime which are controlled by a thermal mechanism (Murray et al., 2000; Fowler et al., 2001), while the temper- J I 20 ate surges were explained by the hydraulic mechanism (Kamb, 1987). Detailed spatial measurements of surge onset are rare due to the difficulty of prediction. The main J I emphasis of many investigations has been on the visible part of the surges. For exam- Back Close ple, several studies have proposed surge initiation during winter (e.g. Raymond, 1987; Echelmeyer et al., 1987; Osipova and Tsvekov, 1991; Eisen et al., 2005; Pritchard Full Screen / Esc 25 et al., 2005). Upglacier propagation of surges from their suggested trigger area has been inferred from upglacier propagation of crevasses (Raymond, 1987; Hodgkins and Printer-friendly Version Dowdeswell, 1994). While mainly focusing on relative changes in surface elevation rather than traditional surge characteristics, Sund et al. (2009) found several early stage Interactive Discussion 4939 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | situations before they had reached the visible and/or advancing stage, and suggested three stages for the active surge phase development. TCD Due to the remote location and large spatial extent of the NGS, satellite remote 7, 4937–4976, 2013 sensing methods are well suited to estimate glacier velocities. In particular, synthetic 5 aperture radar (SAR) satellite sensors are able to penetrate clouds, and the active microwave radar instrument allows observations also during the polar night. Surge dynamics in The surge of NGS enables study of several glacier tributaries subject to relatively the Nathorstbreen similar climate conditions. This study elaborates on surge initiation as well as propaga- glacier system tion in the studied glaciers of NGS and provides new interpretation of surge behaviour. M. Sund et al. 10 We examine the evolution of temporal and spatial distribution of velocities combined with surface elevation changes between 1936 and 2008. The main focus is on glacier dynamics prior to and during the transition to the visible, heavily crevasses advancing Title Page stage. The characteristics of the individual glacier surges are also investigated. Abstract Introduction 2 Background Conclusions References 2 15 The NGS is located in southern Svalbard and covered an area of ca. 430 km prior to Tables Figures the current surge. The glaciers flow from ca. 700 m a.s.l. in the eastern basins and are gently sloping westwards for 20–30 km where they enter Van Keulenfjorden at sea level. J I No previous surges have been observed, yet several historical sources points to such events. Liestøl (1973, 1977) inferred a surge with a maximum extent around 1870 ex- J I 20 tending past the narrowing in the fjord. The Dunér-Nordenskiöld map from 1861–1864 Back Close (Hamberg, 1905) indicate that by then the terminus of the NGS as well as Liestølbreen (Fig. 1) was around 12 km further back in the fjord, than during the advance maximum Full Screen / Esc (Harland, 1997). On Hambergs map (1905) from 1898 an advance had occurred and a calving bay at the terminus indicates a beginning retreat. Folded moraines were also Printer-friendly Version 25 present, and Gripp (1927) took these as indications of glacier advance of these basins. Interactive Discussion Such formations were later viewed as one of the main characteristic of previous surges (Meier and Post, 1969). Even older maps also provide indications of front fluctuations. 4940 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Although they are not were precise, several of the maps back to 1634 presented in Conway (1906) has details showing a narrow passage similar to the current narrow TCD part of the fjord, indicating smaller glacier extent than at present. The maps however, 7, 4937–4976, 2013 do not give any information on which of the glaciers at the head of Van Keulenfjorden 5 were involved in the advances and retreats. Between 1898 and 2002 the joint terminuses of Liestølbreen and Nathorstbreen Surge dynamics in retreated ca. 17.5 km. The retreat rate was greatest around 1958–1961 and corre- the Nathorstbreen sponded well with maximum water depths (Carlsen, 2004). Retreat is common in Sval- glacier system bard surge-type tidewater glaciers during their quiescent phase when ice fluxes are M. Sund et al. 10 low. The joint terminuses of Zawadzkibreen (previously spelled Zawadskibreen), Po- lakkbreen and Nathorstbreen (Fig. 1) started to advance into Van Keulenfjorden during winter 2008–2009, while the first indications of mass displacement appeared already Title Page in 2003 (Sund et al., 2009). Abstract Introduction 3 Data and methods Conclusions References 15 3.1 Satellite data and aerial photos Tables Figures NGS is located along the commercial flight route between Longyearbyen and Tromsø, J I enabling acquisition of detailed images from the air (hereafter these are called images) on clear weather days.